The present invention generally relates to electrochemical cells, i.e., batteries, and, more particularly, to a separator and method of assembly of a separator in an electrochemical cell.
Conventional alkaline electrochemical cells generally include a steel cylindrical can having a positive electrode, referred to as the cathode, which comprises manganese dioxide as the active material. The electrochemical cell also includes a negative electrode, referred to as the anode, which comprises zinc powder as the active material. The cathode is typically formed against the interior surface of the steel can, while the anode is generally centrally disposed in a cylindrical cavity formed in the center of the cathode. A separator is located between the anode and the cathode, and an alkaline electrolyte solution simultaneously contacts the anode, the cathode, and the separator. A conductive current collector is commonly inserted into the anode active material, and a seal assembly, which includes a polymeric seal, provides closure to the open end of the steel can to seal the active electrochemical materials in the sealed volume of the can.
The separator is commonly provided as an ion permeable, non-woven fabric which separates the anode from the cathode. Accordingly, the separator maintains a physical separation of the positive electrode material and the negative electrode material while allowing the transport of ions between the electrode materials. Examples of conventional separator materials include cellophane, nylon, rayon, polyvinyl alcohol (PVA) and cellulose. Separators are usually formed either by preforming the separator material into a cup-shaped basket that is subsequently inserted into the cathode during cell assembly or forming a basket during cell assembly by inserting into the cathode cavity two rectangular sheets of separator material angularly rotated ninety degrees relative to each other. The two sheets are forced into the cylindrical cavity inside the cathode and substantially conform to the cylindrical cavity.
The conventional preformed separator is typically made up of a sheet of non-woven fabric rolled into a cylindrical shape that conforms to the inside wall of the cathode and has a closed bottom end. The closed end is formed by attaching a dielectric material to the bottom end of the separator, such as using a thermoformed hot melt material according to one approach. According to another approach, the closed end is provided by inserting a polymeric seal in the form of a plug in the bottom end of the steel can and inserting the cylindrical separator up against the plug. Yet, another approach includes physically deforming the bottom end of the cylindrical separator by crushing the material at the bottom end into a wad and inserting the separator into the cathode such that the wad forms the closed bottom end.
Many conventional separators do not minimize the amount of material that is disposed in the cell, which can result in reduced volume available for electrochemically active materials. Some conventional separators are susceptible to leaving exposed openings in the separator that may allow for anode-to-cathode contact or anode-to can contact, which prematurely discharges the cell. Further, the preformed separators discussed above require a separate assembly, and therefore require rehandling of the separators which adds to the cost and are susceptible to damage during handling. Accordingly, it is therefore desirable to provide for a separator for use in electrochemical cells that efficiently separates the positive and negative electrodes.